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pacemaker.go
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pacemaker.go
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package hotstuff
import (
"context"
"time"
"github.com/onflow/flow-go/consensus/hotstuff/model"
"github.com/onflow/flow-go/model/flow"
)
type LivenessData struct {
// CurrentView is the currently active view tracked by the PaceMaker. It is updated
// whenever the PaceMaker sees evidence (QC or TC) for advancing to next view.
CurrentView uint64
// NewestQC is the newest QC (by view) observed by the PaceMaker. The QC can be observed on its own or as a part of TC.
NewestQC *flow.QuorumCertificate
// LastViewTC is the TC for the prior view (CurrentView-1), if this view timed out. If the previous round
// ended with a QC, this QC is stored in NewestQC and LastViewTC is nil.
LastViewTC *flow.TimeoutCertificate
}
// PaceMaker for HotStuff. The component is passive in that it only reacts to method calls.
// The PaceMaker does not perform state transitions on its own. Timeouts are emitted through
// channels. Each timeout has its own dedicated channel, which is garbage collected after the
// respective state has been passed. It is the EventHandler's responsibility to pick up
// timeouts from the currently active TimeoutChannel process them first and subsequently inform the
// PaceMaker about processing the timeout. Specifically, the intended usage pattern for the
// TimeoutChannels is as follows:
//
// • Each time the PaceMaker starts a new timeout, it created a new TimeoutChannel
//
// • The channel for the CURRENTLY ACTIVE timeout is returned by PaceMaker.TimeoutChannel()
//
// - Each time the EventHandler processes an event, the EventHandler might call into PaceMaker
// potentially resulting in a state transition and the PaceMaker starting a new timeout
//
// - Hence, after processing any event, EventHandler should retrieve the current TimeoutChannel
// from the PaceMaker.
//
// For Example:
//
// for {
// timeoutChannel := el.eventHandler.TimeoutChannel()
// select {
// case <-timeoutChannel:
// el.eventHandler.OnLocalTimeout()
// case <other events>
// }
// }
//
// Not concurrency safe.
type PaceMaker interface {
ProposalDurationProvider
// CurView returns the current view.
CurView() uint64
// NewestQC returns QC with the highest view discovered by PaceMaker.
NewestQC() *flow.QuorumCertificate
// LastViewTC returns TC for last view, this could be nil if previous round
// has entered with a QC.
LastViewTC() *flow.TimeoutCertificate
// ProcessQC will check if the given QC will allow PaceMaker to fast-forward to QC.view+1.
// If PaceMaker incremented the current View, a NewViewEvent will be returned.
// No errors are expected during normal operation.
ProcessQC(qc *flow.QuorumCertificate) (*model.NewViewEvent, error)
// ProcessTC will check if the given TC will allow PaceMaker to fast-forward to TC.view+1.
// If PaceMaker incremented the current View, a NewViewEvent will be returned.
// A nil TC is an expected valid input.
// No errors are expected during normal operation.
ProcessTC(tc *flow.TimeoutCertificate) (*model.NewViewEvent, error)
// TimeoutChannel returns the timeout channel for the CURRENTLY ACTIVE timeout.
// Each time the pacemaker starts a new timeout, this channel is replaced.
TimeoutChannel() <-chan time.Time
// Start starts the PaceMaker (i.e. the timeout for the configured starting value for view).
// CAUTION: EventHandler is not concurrency safe. The Start method must
// be executed by the same goroutine that also calls the other business logic
// methods, or concurrency safety has to be implemented externally.
Start(ctx context.Context)
}
// ProposalDurationProvider generates the target publication time for block proposals.
type ProposalDurationProvider interface {
// TargetPublicationTime is intended to be called by the EventHandler, whenever it
// wants to publish a new proposal. The event handler inputs
// - proposalView: the view it is proposing for,
// - timeViewEntered: the time when the EventHandler entered this view
// - parentBlockId: the ID of the parent block , which the EventHandler is building on
// TargetPublicationTime returns the time stamp when the new proposal should be broadcasted.
// For a given view where we are the primary, suppose the actual time we are done building our proposal is P:
// - if P < TargetPublicationTime(..), then the EventHandler should wait until
// `TargetPublicationTime` to broadcast the proposal
// - if P >= TargetPublicationTime(..), then the EventHandler should immediately broadcast the proposal
// Concurrency safe.
TargetPublicationTime(proposalView uint64, timeViewEntered time.Time, parentBlockId flow.Identifier) time.Time
}